ARC: Remove explicit passing around of ECR

With ECR now part of pt_regs

* No need to propagate from lowest asm handlers as arg
* No need to save it in tsk->thread.cause_code
* Avoid bit chopping to access the bit-fields

More code consolidation, cleanup

Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
diff --git a/arch/arc/kernel/troubleshoot.c b/arch/arc/kernel/troubleshoot.c
index 9774641..7f85bc3 100644
--- a/arch/arc/kernel/troubleshoot.c
+++ b/arch/arc/kernel/troubleshoot.c
@@ -209,10 +209,9 @@
 }
 
 void show_kernel_fault_diag(const char *str, struct pt_regs *regs,
-			    unsigned long address, unsigned long cause_reg)
+			    unsigned long address)
 {
 	current->thread.fault_address = address;
-	current->thread.cause_code = cause_reg;
 
 	/* Caller and Callee regs */
 	show_regs(regs);